1. Field of the Invention
The present invention relates to a method of manufacturing a magnetic rubber ring, and more particularly to a method of manufacturing a magnetic rubber ring wherein the magnetic rubber ring thus obtained can provide high magnetic forces that are polarized regularly and distributed evenly around its circumference when it is subsequently placed in a magnetic field and then becomes magnetized.
2. Prior Art
A conventional method for manufacturing a magnetic rubber ring of the type referred to above is known, in which an unvulcanized rubber that contains a mixture of an adequate quantity of rubber material and magnetic powders is flattened into a flat rubber sheet by a roll sheeting process. The flat rubber sheet is cut into a square rubber band of a given length having opposite ends cut like slits, and the square rubber band is formed into a rubber band ring by temporarily joining the opposite ends of the square rubber band together. Finally, the rubber band ring is placed in a metal mold where it is compression molded into a finished magnetic rubber ring.
Another conventional method for manufacturing a magnetic rubber ring of the type referred to above is also known. This method, which is more widely used, is designed to provide improved workability and moldability. Specifically, this method consists of using an extruding machine to extrude an unvulcanized rubber containing rubber material and magnetic powders into a rubber band of a given length and having a nearly round cross section, forming a rubber band ring by temporarily joining opposite ends of the rubber band together, and placing the rubber band ring in a metal mold where it is compression molded into a finished magnetic rubber ring.
According to the first mentioned method in which unvulcanized rubber containing an adequate quantity of rubber material and magnetic powders is flattened into a flat rubber sheet by a roll sheeting process, the unvulcanized rubber containing an adequate quantity of rubber material and magnetic powders may inevitably become harder since it originally contains magnetic powders. This is not desirable because a kneading or mixing process for components such as rubber material and magnetic powders can only take place with extreme difficulty. This also applies to the roll sheeting process, where the unvulcanized rubber containing the adequate quantity of rubber material and magnetic powders is flattened into the flat rubber sheet, as well as a process of cutting the flat rubber sheet into a square rubber band of a given length having opposite ends cut like slits. These processes involve much labor and time.
The magnetic powders, such as ferrites, that are contained in the square rubber band normally have poles aligned in an orderly regular fashion, and in one particular direction before it is formed into a rubber band ring. If the square rubber band is twisted inadvertently at or near a middle point thereof when its opposite ends are temporarily joined together to form a rubber band ring, the magnetic powders contained in the rubber band ring would have poles disturbed in a disorderly fashion and oriented irregularly in a circumferential direction of the rubber band ring. Therefore, extreme care is required to ensure that such twisting does not occur at or near the middle point of the square rubber band when the square rubber band is formed into the rubber band ring by temporarily joining the opposite ends of the square rubber band together. This process is not recommended because it must proceed under laborious working conditions as described.
According to the above method, as described above, the magnetic rubber ring may be obtained by cutting the magnetic rubber sheet into the square rubber band having opposite ends cut like slits, forming the square rubber band into the rubber band ring by temporarily joining the opposite ends of the square rubber band together, and placing the rubber band ring into the metal mold where it is compression molded into a finished magnetic rubber ring. This method has a major disadvantage, however, in that when the finished magnetic rubber ring is placed in a magnetic field and is then magnetized, magnetic forces that are produced by the magnetic rubber ring may have poles disturbed in a disorderly fashion and oriented irregularly in a circumferential direction. As a consequence, it is practically difficult to provide a magnetic rubber ring that produces uniform and powerful magnetic forces all over a circumferential direction, when it the ring is placed in a magnetic field and then becomes magnetized.
Thus, it is desirable to provide a method that may provide a magnetic rubber ring that produces uniform and powerful magnetic forces anywhere in a circumferential direction when the ring is placed in a magnetic field and then becomes magnetized.
It may be appreciated from the foregoing description that there are two factors that may potentially cause disturbed magnetic forces in a circumferential direction when a magnetic rubber ring is placed in a magnetic field and then becomes magnetized.
The first factor is that magnetic powders, such as ferrites, that are originally contained in a rubber sheet obtained by a roll sheeting process may have poles that are not oriented regularly.
The second factor is that when a square rubber band is formed into a rubber band ring by temporarily joining opposite ends thereof together, a joint is obtained by simply overlapping slit-like cut faces of opposite ends in a direction in which the ends are compressed, and ferrites contained in a molded rubber band ring may therefore have their pole orientation disturbed at a joint of the opposite ends when the ring is molded, which may cause poles of the ferrites to be oriented irregularly.
As a consequence, it is practically difficult to produce a magnetic rubber ring that provides uniform and powerful magnetic forces all over a circumferential direction of a magnetic rubber ring without disturbing magnetic orientation at a joint of the ring, when the ring is placed in a magnetic field and then becomes magnetized.
Therefore, it is desirable to provide a method that provides a magnetic rubber ring that produces uniform and powerful magnetic forces anywhere in a circumferential direction of the ring when the ring is placed in a magnetic field.
In order to solve the problems described above, a second-mentioned process for manufacturing a magnetic rubber ring is proposed, in which a mixture containing rubber material and magnetic powders, such as ferrites, are extruded into a rubber band by using an extruding machine. This allows ferrites to be aligned in a direction of extrusion.
Even when the above-described extruding machine is used, however, this method has the same problem as does the preceding method. Specifically, when a rubber band obtained by extrusion is formed into a rubber band ring, a joint of the rubber band is obtained by simply overlapping cut faces of opposite ends of the rubber band in a direction in which the rubber band is compressed. This is similar to the rubber band that is obtained by performing the roll sheeting process, and then is cut into a strip of a rubber band having opposite ends cut like slits. Thus, ferrites that are initially aligned and oriented regularly at a time of extrusion molding may be disturbed at a joint of the rubber band when the rubber band ring is formed. When a magnetic rubber ring thus formed is placed in a magnetic field and then becomes magnetized, ferrites contained in the magnetic rubber ring may produce magnetic forces whose orientation is disturbed at a joint of the ring. Thus, uniform magnetic forces in a circumferential direction of a magnetized rubber ring cannot be produced.
In light of the problems of the prior art methods as described above, it is an object of the present invention to provide a method of manufacturing a magnetic rubber ring that can produce uniform and powerful magnetic forces anywhere in a circumferential direction of the ring when it the ring is placed in a magnetic field and then becomes magnetized.
Specifically, the present invention solves those problems by providing a method of manufacturing a magnetic rubber ring, which comprises:
providing an unvulcanized rubber that contains rubber material and magnetic powders;
using an extruding machine to extrude the unvulcanized rubber into a rubber band having a nearly round cross section;
cutting the rubber band having the nearly round cross section into a strip of rubber band having a predetermined length, and forming each of opposite ends of the strip of rubber band so as to have a meeting face slanted at a predetermined angle;
forming a rubber band ring by joining together the opposite ends of the strip of rubber band having respective meeting faces slanted at the predetermined angle; and
compressing, under applied heating, the rubber band ring in a direction of a center line extending through a center of the rubber band ring, and thereby obtaining a finished magnetic rubber ring.
Prior to cutting the rubber band, the predetermined angle, at which the opposite ends of the strip of rubber band are formed to have the respective meeting slanted faces, may be chosen such that the joint between the opposite ends of the strip of rubber band, that is obtained when the strip of rubber band is formed into a rubber band ring, may become thinner in a direction of compression that occurs when the rubber band ring is compressed in the direction of its center line.
The above-described method includes five steps, but this is only shown for purpose of convenience. Cutting the rubber band and forming each of the opposite ends may be separated into two independent steps; that is, a step of cutting and a step of forming. Thus, the method may include the six steps. Additionally, cutting the rubber band and forming each of the opposite ends may be combined with the step of joining the opposite ends together. Thus, the method may include four steps.
Now, the above-described third step through fifth step are described in further detail. A rubber band that is obtained by extrusion, so that the rubber band has a nearly round cross section, is cut into a strip of rubber band having a predetermined length. When the strip of rubber band is formed into a rubber band ring, opposite ends of the strip of rubber band are joined together so that a joint of the opposite ends forms an angle of 20 degrees to 70 degrees with respect to a plane perpendicular to a center line extending through a center of the rubber band ring. Then, in order to compress the rubber band ring into a magnetic rubber ring under applied heating, the ring is placed in a metal mold that includes an upper mold and a lower mold, placed above and below and parallel to the plane perpendicular to the center line of the rubber band ring, in which mold the ring is compressed in the direction of the center line under applied heating.
According to the present invention, a joint of rubber band ring 4 that is obtained by joining opposite ends 5, 6 of strip of rubber band 2a contains the magnetic powders whose poles are oriented relatively regularly, and magnetic rubber ring 24 that results from the rubber band ring 4 also contains magnetic powders whose poles are oriented relatively regularly in a circumferential direction of the magnetic rubber ring.
Accordingly, when the magnetic rubber ring 24 is placed in a magnetic field and then becomes magnetized, the ring can produce powerful magnetic forces that are oriented in one particular direction, and are distributed regularly all over a circumferential direction of the ring.
More specifically, the magnetic rubber ring 24 that is obtained in accordance with the method of the present invention is based on unvulcanized rubber containing any suitable unvulcanized rubber material and any suitable magnetic powders, in which the magnetic powders are originally aligned and oriented relatively regularly in a circumferential direction of a finished magnetic rubber ring 24. Accordingly, when the magnetic rubber ring 24 is magnetized, it can produce powerful magnetic forces that are distributed uniformly all over a circumferential direction of the ring.
Another advantage of the method of the present invention lies in the fact that it can simplify a process of extruding unvulcanized rubber, containing an adequate quantity of rubber material and magnetic powders, into rubber band 2 having a nearly round cross section. This is because when this process takes place, what is required is only to adjust a diameter of the rubber band 2.
A further advantage of the method of the present invention lies in the fact that rubber band 2 has a nearly round cross section. This minimizes a risk of the rubber band 2 being twisted or falling due to misplacement, and facilitates formation of opposite ends 5, 6 of strip of rubber band 2a and joining of the opposite ends for forming rubber band ring 4.
Another advantage of the method of the present invention lies in the fact that it simplifies a process of manufacturing magnetic rubber ring 24, and is easy to perform. Thus, magnetic rubber ring 24 can be produced in a simple and effective manner.